Traditionally, sets of LED drivers are applied to driving display devices, e.g. LEDs and VFDs (vacuum fluorescent displays). The display devices are usually placed in matrix, manufactured in a plane, to create and present planar visual information, like images, pictures, and videos. The display devices discretely represent the pixels of the visual information and are driven by the driving devices. By changing the image data which will be stored in the image data register for each discrete pixel sent to the driving device, the visual content displayed can be varied as desired.
To effectively lower the cost of the driving devices, (for example, to lower the package cost of integrated circuit chips), only limited package pins are applied. Using merely five signal pins and the pins of the exact pin count equal to output port count, the image data are sent to the driving devices which then light the display devices. As shown in FIG. 5, no redundant pins are provided.
The driving devices generally comprise of a current-setting circuit 916, N current-output ports 915, N current-output pins, a serial buffer 911 of N bits, and an image data register 914 of N bits.
The serial buffer 911 conventionally works with three signal pins, clock (CLK), serial-data-in (SDI), and serial-data-out (SDO).
When more than one device works in cascade, the CLK pin in all devices are commonly controlled by a set of synchronous signal sources.
The data in the serial buffer 911 can be transferred to the image data register 914 in parallel, and the transfer is triggered by a signal pin, LE!.
When a signal pin, OE!, receives enable signals, the output ports 915 are capable of delivering driving energy (electrical current or voltage), according to the content in the image data register, at least to light the LEDs.
The content in the image data register can be a set of zeros or ones. If ones represent that the LEDs will be lit, zeroes represent that the LEDs will not be lit, and vice versa.
To improve the accuracy, to give more sophisticated control, and to provide the feedback functions, usually more functional circuitry will be designed and manufactured in the driving devices. However, to exploit these added features, more input pins and output pins will always be required.